Crack Paths 2012

The microscope of analysis is a laser-confocal L E X TOLS2000(LEXT)with maximum

loading weight of 10 kg and a very limited space at the object holder. Furthermore, the

testing machine should provide the possibility of only crack analysis with scanning

electron microscope (SEM).

Subsequently the boundary conditions of the test machine can be summarized as:

• Rotating bending for crack initiation on surface

• Operation under microscope

• Specimens has to be compatible to conventional rotating bending machine

• Test frequency > 5 Hz

• Angle resolution during rotation for positioning of < 1°

• Mounting on L E X Tand S E M

• Easy handling

After virtual design a 3-point bending system with force application emerges from the

other design concepts. With an appropriate specimen shape design, the asymmetric

momentumdistribution due to 3-point-bending is then changed in an axially symmetric

stress distribution over the specimen.

Force application is linked with an on-line monitoring and can apply a maximumforce

of 250 N which e.g. will cause an maximumelastic stress level at the specimens surface

with a testing diameter of 5.5 m mof 765 MPa.

The drive is a special combination of closed loop stepper motor and an planetary gear

(1:5 ratio) to achieve the combination of high stepping resolution (< 0,1°/step) and

moderate test frequency of 10 Hz.

The construction achieves all of the requirements. The dimension of the machine are

335 x 65 x 58 m mwith a weight of 3.2 kg including a steel specimen.

It consists of 4 modules:

1. Drive module

2. Specimen support 1

3. Specimen support 2

4. Force application.

These modules are marked in Fig. 3 by different colouring. For S E Mapplication the

first listed module can be extracted while the remaining modules were bending-resistant

connected. Hence each component is special designed for high vacuum operations with

special features1 except the drive module. In Fig. 3 also the SEM-mounting and the

manufactured prototype is shown. Furthermore, to improve the safety handling, an

operation appraisal was done according to the safety regulations E NISO 13849:2003

and E NISO 12100:2003.

The operating Mini-UBunder the confocal light microscope L E X Tand the individual

programmed easy handling user-interface is shown in Fig. 4 [2].

1 For example one feature is using full ceramic bearings and ultrasonic resistant (for cleaning) force

measuring box for online monitoring.

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